Dominic Sorresso

I like to think that I'm pretty thorough in doing tunes for my car. And like most of you know, once you can do your own cals, the tweaking just never seems to stop. The problem is that we LIKE IT THAT WAY!!
Anyway, one of the things that has continued to annoy me is the tendency of the motor to seesaw a bit coming to a stop in neutral. I didn't have that issue w my 84 Xfire but an LT-5, even stock ones, exhibit that habit to a lesser degree than one that has more aggressive cams and porting. Once I finally got the Injector Bias specs on my 21# injectors, I basically started re-doing the VE tables, particularly at the small PW areas, so naturally decel is one of those areas. I did all the standard stuff smoothing and flattening SA and VE tables around idle, dropped the PG at low air flow, played w IAC. I'm still a bit confused as to the relationship between TF and Min TF tables.
What I seemed to have honed in on is the Closed Throttle VE table (the LT-5 has 4 VE tables for use with secondary ports), and primarily in the cells just somewhat higher than proscribed idle. In my case that's at about 875rpm.
What seems to e working in just the last few cals has been to richen up the cells between 1000-1200rpm and between 20-45kPa by about 6% above where the idle VE is. The motor idles between the 800-900 rpm/50-60kPa.
This seems to calm the decel down and when the car comes to a halt, the idle stays put and doesn't wander. Doesn't seem to buck either at a slow crawl w foot off the accelerator. Much smoother idle.
Any one else have similar experience?

Dominic Sorresso

No comments?

RBob

iTrader: (1)

Seems a reasonable thing to do, if there is an open loop decel that is also helpful. The injector PW gets small so it becomes difficult to get the proportional gains correct.

Recently did something similar to avoid surging on a hot soak restart. The IAT was heat soaking due to the location. This caused the AFR to go a lean and the engine would surge until the IAT cooled off (5 - 10 seconds).

Moved it to a better location which helped quite a bit. But there was still a slight surge or two on a hot start.

So added some fuel to the choke (after-start) AFR table. Calmed it right down. Choke fuel on a hot engine is only there for a very short period of time. But long enough to prevent the slight wave in the engine/RPM.

RBob.

Dominic Sorresso

Thanks RBob. I have run into the surge just after re-start on a hot motor also.
Will try a bit more choke.
If there's an O/L Decel, I don't see it in the mask. There is a
C/L TPS% for idle(6B2), but I am assuming that's max TPS% before going out of ECM idle control. However, there's also an IAC Max TPS% for Idle (7C7). Sounds redundant but maybe not.

RBob

iTrader: (1)

The TPS% value at $6B2 is used for the closed loop table look ups. Such as the three O2 window tables, the slow O2 filter look up, INT delay and proportional gains. When in idle from that TPS% and the MPH parameter ($6B3), the airflow is set to 0 for the look ups.

The TPS% value at $7C7 ($7C4?) is used for idle SA stabilization among some other things.

I didn't go through the option flag words too much, so don't know if there is an open loop decel or idle option.

RBob.

Dominic Sorresso

That 7C7 address could be a little different depending on which mask you're looking at.
The "A" versions of the calibration seem to skew the addresses by 3, so the 7C7 v 7C4 is possible.. I'm using the $D0A mask.
I'm wondering if 1.95% may be too large a TPS opening for airflow to be 0gms. These LT-5s will suck the vinyl off a binder at an 850rpm closed throttle idle. Almost literally rip it off when binder is up against the throttle body checking for vacuum leaks.
There is 't much in the way of Option Words in the cal I have except for Closed Throttle SA.

lakeffect2

Related to the heat soak issues. Move a new sensor (plastic birdcage type) into the air filter just before the throttle body. Leave the old sensor in the hole to keep the old hole plugged, but unplug the wire, and lengthen the wires to reach forward. You only need a few feet of wire and four butt connectors. I use a K&N RC5000 filter, so I simply drilled a hole for the new sensor position in the rubber mounting flange.

The factory mounting positionseems to be a problem for me for around town driving. You leave home, drive to the store, shop for a few minutes and come back out. What you get next is a heat soaked metal air temp sensor sending the info about how hot your heat soaked plenum is, not the air temp. And it seems to stay hot for a long while

. I also moved the Ignition module out of the distributor to the fender well for the same reason. When Left in the distributor, it's above a hot engine and hotter exhaust manifolds. After moving it, and sandwiching it with some computer cooling fins, no more ignition problems either.

Hope this helps some of you.

Dave Buchholz

RBob

iTrader: (1)

I recall the 3 byte offset, but wasn't sure exactly where it was.

As for the airflow being set to 0 during idle. This is done to use the first entry of the various tables. It is a way to not have to use separate values in place of the tables when at idle. The actual airflow doesn't matter.

RBob.

RBob

iTrader: (1)

I'm using the over-the-radiator 2.8l V6 air cleaner set up. This places the IAT right on top of the radiator, I figured it would heat soak.

It is now over by the CCP canister more in the open air. The plan is to get one of the grommet mount IATs and place it in the air box where it is out in front of the car. I don't want to mount the heavy threaded sensor there.

But that may also pickup heat soak as it is in front of the radiator. Just need to try it.

Getting the ICM out of the distributor is helpful. I added a heat sink to the bottom of the distributor under the ICM.

RBob.

Dominic Sorresso

RBob,

The 3 byte offset starts in the x7xx address range for the "A" masks.

TT 68

Great ideas Dave. Thanks for sharing. I always thought that was a bad place to put the ignition module. It is only there because it is cheap and easy to do. Cool electronics live a longer happier life so the relocation with the addition of some cooling fins and heat sink should be an improvement to reliability.

If I remember right one of the distributor connectors shares the same exact connector as one of the transmission connectors. It's been a long time so I can't remember which one it was or what application but if that can be figured out it could be a source for a good length of donor wire with the correct connector for relocating the ignition module out of the heat soaked distributor and off of the hot engine. I think it was one of the 4L80E connectors.

Dominic Sorresso

The picture of my motor shows an MAT mounted in the airborne, which is the stock placement. My IAT is positioned ahead of the intake bellows in the air intake downstream of the radiator. Drilled a hole in the plastic intake and used a grommet for mounting plastic IAT. BTW, RBob, trying out your crank fuel idea for hot re-start.

Dominic Sorresso

Just went out for a drive after having added a bit more fuel in those areas just above the idle rpm and at just lower MAP than idle. I can't say this is anything like Grumpy's Final Answers, BUT if you are dealing w same symptoms of surging idle during freewheeling decel, let me recommend you try this.
What's really neat is how the idle settles down immediately once stopped and just sits there.

Dominic Sorresso

The surging has really been diminished at this point. There is a bit but no longer annoying. Maybe one or two slight blips but much more subdued. And once I am below the Idle MPH param, the idle is well stabilized.
However, one small observation, is that I can see on my WB the AFR INCREASING to 16-17 briefly on closed throttle, then stabilizing back to a 14.5-15.3 back and forth, which I assume is the prop gain doing what it does.